1. Field of Invention
The present invention relates to an optical modulation device and a projection display device utilizing the optical modulation device, and more particularly, to a technique for achieving a reduction in size and for efficiently cooling an optical system including the optical modulation device arranged inside the device.
2. Description of Related Art
Hitherto, a projection display device has been known which includes a light source lamp, an optical system for optically processing light emitted from the light source lamp so as to form an optical image according to image information, a projection lens for enlarging and projecting the image formed by the optical system onto a projection plane, and a power supply for supplying electric power for driving the device. In such a projection display device, the optical system usually includes a color separation optical system for separating light from the light source lamp into three colors, optical modulation devices for respectively modulating the separated three color light, and a prism unit for synthesizing the modulated light. In addition, the optical modulation devices are arranged on a head member of high rigidity inside the device so that the images formed by three optical modulation devices are not be projected offset from one another.
In addition, such a projection display device is widely utilized in multimedia presentations at conferences, academic meetings, exhibitions, and the like.
Incidentally, the projection display device may be kept installed in a conference room, or the like for a presentation, but may be brought in the meeting room as necessary, or stored in another place after the presentation. Therefore, it is necessary to improve portability in order to facilitate transportation of the device, and a further reduction in size is demanded. On the other hand, however, a light source tends to be intensified in order to secure luminance of a projected image.
However, a reduction in size of the device allows various types of components to be densely arranged in the device, and it is difficult to circulate cooling air drawn ill by a fan or the like. In addition, since the optical modulation devices are easily affected by heat, it becomes important to effectively cool heat-generating components, and to prevent the optical modulation devices from storing heat.
It is an object of the present invention to provide an optical modulation device which can facilitate a reduction in size of the device and achieve the prevention of overheating of the device, and to provide a projection display device utilizing the optical modulation device.
An optical modulation device of the present invention may consist of an electro-optical device for modulating light emitted from a light source according to image information, wherein a sapphire glass is affixed to at least one surface of the light-incident side and the light-emitting side of the light of the electro-optical device.
Further, the optical modulation device of the present invention may consist of an electro-optical device for modulating light emitted from a light source according to image information, wherein the electro-optic device has a pair of substrates, and at least one of the substrates is made of sapphire glass having a thickness of not less than 1.5 mm, and not more than 3 mm.
A comparison of characteristics of the sapphire glass and characteristics of other glasses is given in Table 1.
As will be understood from Table 1, the thermal conductivity of the sapphire glass is extremely high. Therefore, according to the present invention, the heat-dissipating property of the optical modulation device is improved, and overheating can be prevented. In addition, this enables the use of a light source having higher luminance. Further, since the light from the light source can be collected on the optical modulation device having a smaller area, the optical modulation device can be reduced in size.
Further, by affixing a sapphire glass to the electro-optical device, dust can be prevented from being attached to the electro-optical device.
In addition, since the sapphire glass is hard because of high Young""s modulus, and is difficult to scratch, yield thereof is improved and it becomes easy-to-handle, thereby facilitating management.
In addition, in the case where the optical modulation device of the present invention is used in the projection display device, when the sapphire glass is affixed to the light-emitting surface of the electro-optical device, by increasing the thickness of thereof larger than the focal depth of the projection lens, or when the substrate is made of sapphire glass, by setting the thickness thereof to not less than 1.5 mm, and not more than 3 mm, dust or the like attached to the surface thereof can be made inconspicuous on the projection screen. Here, since the sapphire glass has a high refractive index as shown in Table 1, in the case where the sapphire glass is used for such a purpose, sapphire glass thinner than other glasses can be used.
Further, in the electro-optical device having pixels formed in a matrix, and the periphery of the pixels is light-shielded, a micro lens array may be provided on the light-incident surface. The micro lens array is intended for improving the use efficiency of light by collecting light to a portion (opening) where the pixels are not shielded so that the incident light is not shielded by a light-shielding section. In the present invention, when the sapphire glass is affixed to the light-incident surface of the electro-optical device, or when the substrate of the electro-optical device on the light-incident side is made of sapphire glass, the sapphire glass may be used as the micro lens array. As will be understood from Table 1, since the sapphire glass has an extremely high refractive index, a sufficient light-collecting power can be obtained even without reducing a radius of curvature of the micro lens. Therefore, the micro lens can be accurately formed, thereby making it possible to more effectively achieve improvement in the use efficiency of light. Further, in the case where the optical modulation device provided with the micro lens array is used in the projection display device, even if light having a large angle of incidence enters the optical modulation device, the use of the sapphire glass as the micro lens array allows the light to be corrected to light having a smaller angle of incidence. Therefore, the amount of light taken by the projection lens can be increased, thereby making it possible to obtain a bright projection image.
In the optical modulation device of the present invention, the sapphire glass may be preferably affixed to the surface of the light-incident side of the electro-optical device. Alternatively, the substrate on the light-incident side of the electro-optical device may be preferably made of sapphire glass because, as described above, the sapphire glass can be used as the micro lens array in this case. In addition, in the case where the optical modulation device of the present invention is adopted to the projection display device using the cross-dichroic prism, as in the embodiments of the present invention to be described later, since the light-incident side has more spaces and provides higher heat-dissipating effect than the light-emitting side, overheating of the optical modulation device can be prevented more efficiently.
The optical modulation device of the present invention may preferably include a frame for holding the electro-optical device, and a metal thin-film may be preferably provided on a contact portion between the frame and the sapphire glass. In this case, since heat is transmitted to the frame via the metal thin-film, heat-dissipating property is further improved, and the overheating of the optical modulation device can be prevented more efficiently.
In addition, the frame may be constructed to have two frames for holding the electro-optical device from the side of the light-incident surface and the side of the light-emitting surface. In this case, at least one of the frames may be preferably formed of a material including magnesium having excellent thermal conductivity and heat-dissipating property as a principal material. In addition, heat-dissipating fins may be preferably provided on the frame, and the fins may be preferably provided along the flow of cooling air for cooling the electro-optical device and the vicinity thereof. This allows heat to be discharged from the frame more excellently, thereby preventing overheating of the optical modulation device more efficiently.
In the optical modulation device of the present invention, a graphite sheet for transmitting heat from the frame to another part may be provided on the frame. In this case, the graphite sheet may be connected to a metallic part. Since the graphite sheet has good thermal conductivity, heat from the optical modulation device can be transmitted to other parts. In particular, by bringing it into contact with the metallic part, the overheating of the optical modulation device can be prevented more efficiently.
Further, in the optical modulation device of the present invention, when polarizers are arranged on the light-incident side and light-emitting side of the electro-optical device, at least one of the polarizers may preferably be arranged at a position apart from the electro-optical device or the sapphire glass. This can prevent the heat generated on the polarizers from being transmitted to the electro-optical device and the sapphire glass.
The projection display device of the present invention may consist of three optical modulation devices for respectively modulating red, green, and blue light according to image information, wherein the optical modulation devices have an electro-optical device, and wherein a sapphire glass is affixed to at least one surface of the light-incident side and the light-emitting side of the light of the electro-optical device in the optical modulation device for modulating at least blue light.
In addition, the projection display of the present invention may consist of three optical modulation devices for respectively modulating red, green, and blue light according to image information, wherein the optical modulation devices have an electro-optical device, wherein the electro-optical device has a pair of substrates, and wherein at least one of the substrates of the electro-optical device in the optical modulation device for modulating at least blue light is made of sapphire glass having a thickness of not less than 1.5 mm, and not more than 3 mm.
As will be understood from Table 1 give above, the thermal conductivity of the sapphire glass is extremely high. Therefore, if the sapphire glass is affixed to the electro-optical device, or if at least one of a pair of substrates of the electro-optical device is made of sapphire glass, heat-dissipating property of the optical modulation device is improved, and overheating can be prevented. Thus, of the optical members constituting the projection display device, the electro-optical device particularly having poor heat resistance is easily cooled, and reliability of the device is improved. Here, the above-described configuration can be applied to all of the optical modulation devices for the three colors. However, only by applying blue light having the highest energy to the optical modulation device that modulates and by the optical modulation device being easily deteriorated thereby, the effect of improvement of reliability of the device can be expected. In addition, the configuration may be mounted to only the optical modulation device modulating any two colors. In this case, the configuration may be applied to the optical modulation devices that modulate blue and green colors having relatively high energy.
In addition, since the electro-optical device can be easily cooled, a light source having higher luminance can be used, and a projection display device of a bright image can be obtained. Further, since the light from the light source can be collected on the optical modulation device having a smaller area, the device can be reduced in size.
In addition, the sapphire glass is hard because of high Young""s modulus, and is difficult to be scratched. Therefore, deterioration in image quality due to projection of scratch on the projected image can be prevented.
Further, by affixing the sapphire glass on the light-emitting surface of the electro-optical device to increase the thickness thereof to larger than the focal depth of the projection lens, or by making at least one of a pair of substrates of the electro-optical device of sapphire glass having a thickness of not less than 1.5 mm, and not more than 3 mm, dust or the like attached to the surface thereof can be made inconspicuous on the projection screen. Here, since the sapphire glass has a high refractive index as shown in Table 1, in the case where the sapphire glass is used for such a purpose, sapphire glass thinner than other glasses can be used. Thus, the heat from the electro-optical device is discharged to the outside with extreme efficiency as compared with other glasses.
Further, as described above, when the sapphire glass forming the micro lens array is affixed to the light-incident surface of the electro-optical device, or when the substrate on the light-incident side is made of sapphire glass, even if light having a large angle of incidence enters the optical modulation device, it can be corrected to light having a smaller angle of incidence. Therefore, the amount of light taken by the projection lens can be increased, thereby making it possible to obtain a bright projection image.
In the projection display device of the present invention, the sapphire glass may be preferably affixed to the surface of the light-incident side of the electro-optical device. In addition, when the substrate is made of sapphire glass, the substrate on the light-incident side may be preferably made of sapphire glass because the sapphire glass can be used as the micro lens array in this case. In addition, in a projection display device using the cross-dichroic prism, as in the embodiments of the present invention to be described later, since the light-incident side has more spaces and provides higher heat-dissipating effect than the light-emitting side, cooling of the optical modulation device can be further facilitated.
The projection device of the present invention may preferably include a frame for holding the electro-optical device, and a metal thin-film may preferably be provided on a contact portion between the frame and the sapphire glass. In this case, since heat is transmitted to the frame via the metal thin-film, cooling efficiency of the optical modulation device can be further improved, thereby further contributing reliability of the device.
In addition, the frame may be constructed to have two frames for holding the electro-optical device from the side of the light-incident surface and the side of the light-emitting surface. In this case, at least one of the frames may preferably be formed of a material including magnesium having excellent thermal conductivity and heat-dissipating property as a principal material. In addition, heat-dissipating fins may be preferably provided on the frame, and the fins may be preferably provided along the flow of cooling air for cooling the electro-optical device and the vicinity thereof. This allows cooling efficiency of the optical modulation device to be improved more efficiently, thereby further improving reliability of the device.
In the projection display device of the present invention, a graphite sheet for transmitting heat from the frame to another part may be provided on the frame. In this case, the graphite sheet may be connected to a metallic part. Since the graphite sheet has good thermal conductivity, heat from the optical modulation device can be transmitted to other parts. In particular, by bringing it into contact with the metallic part, the cooling efficiency of the optical modulation device can be further improved.
Further, in the projection display device of the present invention, when polarizers are arranged on the light-incident side and the light-emitting side of the electro-optical device, at least one of the polarizers may be preferably arranged at a position apart from the electro-optical device or the sapphire glass. This can prevent the heat generated on the polarizers from being transmitted to the electro-optical device and the sapphire glass, thereby further improving the cooling efficiency of the optical modulation device.